Alopecia
Basics
Absence of hair from areas where it normally grows
Description
- Phases of the hair follicle cycle
- Anagen phase (growth phase): 90% scalp hair follicles, lasts 2 to 6 years
- Catagen phase (transition phase): regression of follicle, <1% follicles, lasts 3 weeks
- Telogen phase (resting phase): club hair ready for shedding, lasts 2 to 3 months
- Scarring (cicatricial) alopecia
- Inflammatory disorders leading to permanent follicle destruction and hair loss
- Includes lymphocytic, neutrophilic, and mixed cicatricial alopecia
- Nonscarring (noncicatricial) alopecia
- Mild or no inflammation, no destruction of follicle
- Includes focal (alopecia areata [AA], traction alopecia), patterned (androgenic alopecia, female pattern hair loss), or diffuse hair loss (telogen effluvium, anagen effluvium)
- Structural hair disorders: Brittle hair from abnormal hair formation/external insult
Epidemiology
Prevalence
- Androgenic alopecia:
- In males, 30% Caucasian by 30 years of age, 50% by 50 years of age, and 80% by 70 years of age
- In females, 70% of women >65 years of age
- AA: 1/1,000 with lifetime risk 1–2%; men and women are affected equally.
- Scarring alopecia: rare, 3–7% of all hair disorder patients
Etiology and Pathophysiology
- Scarring (cicatricial) alopecia
- Inflammatory disorders leading to permanent destruction of the follicle
- Slick smooth scalp without follicles evident
- Three subtypes based on inflammation: lymphocytic, neutrophilic, and mixed
- Primary scarring includes discoid lupus, lichen planopilaris, frontal fibrosing alopecia, central centrifugal cicatricial alopecia, acne keloidalis nuchae, folliculitis decalvans, dissecting cellulitis of scalp, primary fibrosing, among others
- Secondary scarring from infection, neoplasm, radiation, surgery, and other physical trauma, including tinea capitis
- Central centrifugal cicatricial alopecia is the most common form of scarring hair loss in African American women; etiology unknown but possibly from hair care practices
- Nonscarring (noncicatricial) alopecia
- Focal hair loss
- AA: patchy hair loss, usually autoimmune, T cell–mediated inflammation resulting in premature transition to catagen and then telogen phases
- May progress to alopecia totalis (entire scalp) or alopecia universalis (loss of all hair)
- Nail disease frequently seen (10–20% of patients with AA)
- High psychiatric comorbidity
- Alopecia syphilitica: “moth-eaten” appearance, secondary syphilis
- Pressure-induced alopecia: hair loss from long periods of pressure on one area of scalp
- Temporal triangular alopecia: congenital patch of hair loss in temporal area
- Traction alopecia: due to physical stressor of tight braids, ponytails, hair weaves
- AA: patchy hair loss, usually autoimmune, T cell–mediated inflammation resulting in premature transition to catagen and then telogen phases
- Patterned hair loss
- Androgenic alopecia: hair transitions from terminal to vellus hairs
- Male pattern hair loss: thinning in bitemporal or vertex areas (Hamilton-Norwood Scale, stages I to VII); results from increased androgen receptors, and increased 5-α reductase leads to increased testosterone conversion in follicle to dihydrotestosterone (DHT); this leads to decreased follicle size and vellus hair
- Female pattern hair loss: thinning on frontal and vertex areas; unclear etiology, possible association with polycystic ovarian syndrome, adrenal hyperplasia, and pituitary hyperplasia
- Trichotillomania: intentional pulling of hair from scalp; presents various patterns
- Focal hair loss
- Diffuse
- Telogen effluvium: sudden shift of many follicles from anagen to telogen phase, resulting in decreased hair density but not bald areas
- May follow major stressors, including childbirth, injury, illness; occurs 2 to 3 months after event
- Can be chronic with ongoing illness (SLE, renal failure, IBS, HIV, thyroid/pituitary dysfunction)
- Adding or changing medications (oral contraceptives, anticoagulants, anticonvulsants, SSRIs, retinoids, β-blockers, ACE inhibitors, colchicine, cholesterol-lowering medications, etc.)
- Malnutrition from malabsorption, eating disorders; poor diet can contribute.
- Anagen effluvium
- Interruption of the anagen phase without transition to telogen phase; days to weeks after inciting event
- Chemotherapy is the most common trigger. Radiation, anticancer drugs, and severe protein-calorie malnutrition can also trigger.
- Telogen effluvium: sudden shift of many follicles from anagen to telogen phase, resulting in decreased hair density but not bald areas
- Inherited and acquired structural hair disorders
- Multiple inherited hair disorders including Menkes disease, monilethrix, and so forth; these result in the formation of abnormal hairs that are weakened.
- May also result from chemical or heat damaging from hair processing treatments
Genetics
Family history of early patterned hair loss is common in androgenic alopecia, also in AA.
Risk Factors
- Genetic predisposition
- Chronic illness including autoimmune disease, infections, cancer
- Physiologic stress including pregnancy and childbirth
- Poor nutrition
- Medication, chemotherapy, radiation
- Hair chemical treatments, braids, weaves/extensions
General Prevention
Minimize risk factors if possible.
Commonly Associated Conditions
- See “Etiology and Pathophysiology.”
- Vitiligo—4.1% patients with AA, may be the result of similar autoimmune pathways
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Citation
Domino, Frank J., et al., editors. "Alopecia." 5-Minute Clinical Consult, 33rd ed., Wolters Kluwer, 2025. Medicine Central, im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688645/all/Alopecia.
Alopecia. In: Domino FJF, Baldor RAR, Golding JJ, et al, eds. 5-Minute Clinical Consult. Wolters Kluwer; 2025. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688645/all/Alopecia. Accessed October 10, 2024.
Alopecia. (2025). In Domino, F. J., Baldor, R. A., Golding, J., & Stephens, M. B. (Eds.), 5-Minute Clinical Consult (33rd ed.). Wolters Kluwer. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688645/all/Alopecia
Alopecia [Internet]. In: Domino FJF, Baldor RAR, Golding JJ, Stephens MBM, editors. 5-Minute Clinical Consult. Wolters Kluwer; 2025. [cited 2024 October 10]. Available from: https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688645/all/Alopecia.
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